Grinding wheel feeding mechanism



May 23, 1944.

C. G. FLYGARE ET AL GRINDING WHEEL FEEDING MECHANISM V Filed Feb-.- 12, 1942 Yb WW CARI.

WALTER F. hlcu uvsulv Patented May 23, 1944 GRINDING WHEEL FEEDING MECHANISM Carl G. Flygare and ,Walter F. Johnson, Worcester, Mass., assignors to Norton Company,

corporation of Massachu- Worcester, Mass, a setts Application February 12, 1942, Serial No; 430,664

Claims.

The invention relates to grinding machines,

and more particularly to a control mechanism for an hydraulically operated grinding wheel feeding mechanism. One object of the invention is to provide a simple and thoroughly practical hydraulically operated grinding wheel feeding mechanism for a grinding machine. Another object of the invention is to provide a wheel feed controlling mechanism which is arranged so that the grinding wheel may be fed rapidly as it is moved into operative engagement with the work, then at an initial grinding speed, after which the infeed is reduced to a very fine infeed.

A further object of the invention is to provide a wheel feeding mechanism with a normal grinding infeed which is automatically changed when the wheel reaches a predetermined position, to a fine infeed, after which a positive stop positively prevents further infeeding movement of the wheel. Another object of the invention is to provide a dash pot wheel feed controlling mechanism with a pair of control valves, both of which serve to control the initial grinding feed, after which one of the valves is cut off and the second valve controls a very fine infeeding movement of the grinding wheel.

Another object of the invention is to provide a dash pot feed control mechanism with two cont-rol valves, one for regulating the initial grinding feed and the other for regulating the final infeeding movement of the Wheel combined with an electrically controlled valve which is closed when the second feed control'valve is rendered operative to prevent leakage of fluid from the dash pot controlling mechanism through the first named valve. Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements,

away and shown in'section, combined with a hydraulic piping and wiring diagram.

A grinding machine has been illustrated in the drawing comprising a base I0 which suDPOrts a transversely movable wheel slide II which is mounted on transversely extending ways (not shown) on thebase In. The Wheel slide ll supports a rotatable grinding wheel I2 which is mounted on the end of a rotatable wheel spindle 13; The wheel spindle l3 may be driven by any of the well known mechanisms, such as an overhead belt driveor an electric motor l6 mounted on the wheel slide. As illustrated, a wheel driving pulley I4 is mounted on the opposite end of the wheel spindle l3 and is connected by a driving belt with a pulleyon the electric motor IS.

The base It! also supports a longitudinally movable work table I! which is arranged to reciprocate longitudinally relative to the base ID on a fiat way l8 and a V-way IS. The table II is provided with a rotatable work support including a headstock and a footstock (not shown) each of which is provided with work supporting centers rotatably to support a work piece 2! in operative relation with the grinding wheel 12. The table I! may be traversed longitudinally by a manually operable traverse mechanism which includes a rack bar depending from the under side of the table :1. The rack bar 25 meshes with a gear 26 mounted on the inner end of a rotatable shaft 21. A manually operable traverse Wheel 28 is mounted on the outer end of the shaft 27 and is arranged to be manually rotated to traverse the table I! longitudie nally relative to the base It]. If desired, a power operated table traversing or reciprocating mechanism may be provided, such as for example a mechanisim of the type shown in the expired United States patent to Norton No. 762,838 dated June 14, 1904.

A wheel feeding mechanism is provided for manually feeding the grinding wheel toward and from the work, which comprises a half nut depending from the wheel slide l I. The half nut 35meshes with or engages a rotatable cross feed screw 36. Avforwardly extending portion 31 of the cross feed screw 36 is slidably keyed to a rotatable sleeve-38. The rotatable sleeve 38 is formed as an integral part of a rotatable shaft which is mounted in bearings 39 and 40 in the base H]. A manuallyoperable feed wheel 4| is mounted on the outer end of a stud 42. The stud 42 carries a pinion 43 which meshes with a gear 44 mounted on the outer end of a sleeve shaft 38 so that a manual rotation of the feed wheel 4| serves to rotate the feed screw 36 in either direction to cause a forward or rearward feeding movement of the grinding wheel l2 and the wheel slide H. The wheel feed 4| may be provided with a micrometer adjusting mechanism 45 which is substantially identical with that toremain in their rearmost position.

shown in the above-mentioned prior United States patent to Norton. This micrometer mechanism serves precisely to adjust a stop abutment relative to the manually operable infeed wheel to compensate for wheel wear.

In the preferred construction the wheel slide ii is arranged so that it may be moved toward and from the work piece 2| to grind the same to a predetermined size by means of a fluid pressure actuated wheel feeding mechanism. As illustrated in the drawing, the rear end of the feed screw 36 is rotatably supported in a slidably keyed bearing 50 which is supported in a casing El on the base of the machine. A fluid pressure cylinder 49 is attached to the casing 5| and contains a slidably mounted piston 52 which is connected by a piston rod 53 with the bearing 50 and is arranged so that when fluid under pressure is admitted to a cylinder chamber 54, the piston 52 will be moved toward the right into its rearward position, as illustrated in the drawing, transmitting a corresponding movement through the feed screw 36, the half nut 35, to move the wheel slide H and the grinding wheel l2 rearwardly to an inoperative position. when fluid under pressure is admitted to the cylinder chamber 54 or the cylinder chamber 55, a rapid approaching or receding movement of the grinding wheel I?! and wheel slide H is provided. I

A fluid pressure system is provided to supply fluidunder pressure for moving the piston 52 so as to cause an infeeding or outfeeding movement of the grinding wheel l2. This system may comprise a reservoir 60 which is formed as a boxthe pipe 63 enters a valve chamber re located between the valve pistons 61 and t8 and passes through a passage '42, into the cylinder chamber St, to move the piston 52 to its rearward position with the-grinding wheel is separated from the .work piece 2 i, as indicated in the drawing. During the rearward movement of the piston 52 to ward the right, fluid is exhausted from the cylinder. chamber 55, through a passage it, into a valve'chamber ll, between the valvefpistons 65 and 6?, and out through a pipe it which exhausts into the reservoir Ell.

' The valve stemfifi is arranged so that it may be moved endwise to shift the valve 6 3 into a reverse position so as to cause either a forward or rearward feeding movement of the grinding wheel I2. In thepreferred construction a spring 80 is provided to maintain the valve 64 normally in its right-hand end position to cause the piston 52 and wheel slide II and grinding wheel I2 I A solenoid 8i mounted on the base H] is provided to shift the valve 64 toward the left to cause a forward feeding movement of the grinding wheel l2 when desired. The solenoid 8| is connected by a link 82 with a stud 83 supported at the lower end of a rock armtfil. The rock arm fi lis pivotally supported by astud 85 which'is supported by. a bracket 8%;fastened to the base id of the machine. The upper end of the rock arm 84 isprovided with a stud El which rides within an annular groove formed in a spool-shaped Similarly, I

member 88 supported on the lefthand end of the valve stem 65.

A suitable fluid pressure controlled or feed regulating mechanism is provided for modifying the rapid approaching movement caused by the piston 52 to obtain a controlled and predetermined infeeding movement of the grinding wheel [2. In the preferred construction a self-contained dash pot feed regulator is provided comprising a pair of dash pot cylinders 36 and 9? which contain dash pot pistons 98 and 99, respectively. The dash pct pistons 98 and 99 and their respective cylinders 56 and 9'! are arranged with their axes parallel to each other and spaced on diametrically opposite sides of the piston rod 53. The dash pot pistons 98 and 99 are normally held in a rearward (right-hand) position by means of springs it!) and Ifll, respectively. An

adjustable stop screw H32 serves to limit the rearward movement of the dash pot pistons 98 and $9, respectively. A slidable sleeve N13 is supported on the rear extension 53a of the piston rod 53. The sleeve N33 has a flanged portion I04 which is either formed integral therewith or fixedly secured thereto. The flange N34 is arranged to engage the right-hand end faces of the dash pot pistons 98 and 99, respectively. The stop screw'l lt engages the flange lil l and thereby serves to limit the rearward movement of the dash pot pistons 93 and 99 toward the right.

The rapid forward feeding movement of the grinding wheel L2 and wheel slide H continues until the adiustablenuts I05 on a threaded portion it of the extension 530 of the piston rod 53 engages the right-hand end of the sleeve I03. Continued movement of the piston rod 53a moves the sleeve' Hi3 and the flange I04 toward the left and continued movement serves to move [the dash pot pistons 98 and 99 in a direction toward the left. When the flange lil l engages the ends of the dash pot pistons 98 and 99, respectively, the rapid approaching or feeding movement of the grinding wheel l2 toward the work piece H, as produced by the piston 52, is reduced to a slower predetermined grinding feed due to thefact that fluid confined within the dash pot cylinders and 91', respectively. which are interconnected, exhausts through a passage lfl'l, a needle valve H38, through a pipe [69, into a reservoir Hi]. By adjusting the aperture of the needle valve H38, a desired and predeterminedv infeeding movement of the grinding wheel I2 may be obtained.

When fluid under pressure is admitted to the cylinder chamber 54 to cause a rearward move,- ment of the piston 52, the sleeve I63 together with the flange Hi l, is moved rearwardly by means of the released compression of the springs I00 and I ill which'returns the dash pot pistons 98 and 99, respectively, to their rearward positions and moves the flange [M and its supporting sleeve I03 toward the right until the flange I04 engages the adiustable'stop screw m2. During the rearward movement of the dash pot pistons 93 and 99, a suction is created within the dash pot cylinders 96 and 97, respectively, which serves to aid in drawing fluid from the reservoir H0, through a pipe I l l; and a ball check valve I 82, to fillthe dash pot cylinder chambers SEiand 91 for the next infeeding. movement of the grinding wheel I2. During theinfeeding movement of the dash pot pistons 98 and 99, fluid within the dash pot cylinders 96 and 9"! servesto hold the ball check valve H2 closed so that fluid within the: dash pot cylinders 96 and 91 is forced out through the passage I01 and the needle valve I08, into the reservoir H0, to control the rate of the infeeding movement, as desired; An ad justable throttle valve H1 is provided to facilitate the exhaust of fluid from the dash pot chambers 96 and 91 after the port or passage I8? is closed by the piston 98. If desired, the needle valve IIlB may be utilized to attain a final or finish grinding operation which is terminated when a positive stop collar H3 engages a stop surface I I4 formed on the end plate enclosing the, dash pot cylinders 98 and 91.

.' In certain grinding operations it is desirable to; feed the grinding wheel into the work to reduce it to approximate size, after which the feeding movement of the grinding wheel is further slowed down or reduced to an extremely fine feed justprior to positively stopping the infeed by engagement of the stop collar H3 with the stop surface H4. This may be accomplished by providing an adjustable throttle valve Ii'i which is arranged to control the exhaust of fluid. from the dash pot cylinders 96 and 91 after the port or passage I 8'! is closed by the forward movement of the dash pot piston 98. It will be readily apparent from the foregoing disclosure that the valve HT may be entirely closed, in which case the needle valve I08 will control the entire infeed of the grinding wheel or, when desired, the throttle valve II'I may be opened to the desired extent so that after the closing of the port or passage I01, the valve III will control exhaust of fluid from the dash pot cylinders 813 and ill, thu facilitating an extremely fine precise feeding movement of the grinding wheel I2.

During the veryfine final infeed of the grinding wheel I2, it is desirable that no fluid leak through the port or passage I01 and the needle valve I08. It is, therefore, desirable to provide a shut-off valve H8 having a, movable cone-shaped frusto-conically shaped valve member H9 which is normally held in engagement with a valve seat I20 by means of a spring I2I. The valve H8 is arranged so that when it is closed, no fluid can pass through the port I 01 and valve I08 and from pipe I09 into pipe I09a into reservoir H8. A solenoid I22 is of the pull type which is arranged when energized to open the valve H8, that is, move the valve parts into the position illustrated in the drawing against the compression of the spring I2I. A normally closed limit switch I23 is provided for controlling the solenoid I22. During the rapid approach and the initial grinding feed, the switch I23 remains closed to energize the solenoid I22 and to hold the valve H8 open.

' An adjustable stop screw I24 is carried b a bracket I 25 which is fixedly mounted on the stop collar H3. The stop screw I24 is arranged to move in the path of an actuating plunger I26 of the limit switch I23. Th crew I24 is preferably adjusted so that when the valve piston 98 closes the port I81, the screw I24 will engage the plunger I26 and open the switch I23, thus deenergizing the solenoid I 22 so that the released compression of the spring I2I will close the valve H8 so that no fluid leaking by the dash pot pistons may escape through the port Ill! and valve I08 and pipe I09 into the pipe IBM and reservoir I I0. After the valve I I8 closes, all fluid exhausting from the dash pot cylinders must pass through the adjustable valve I I! which may be set to provide an extremely fine final feeding movement of the grinding wheel which continues until the stop collar H3 engages the stop surface H4,

The forward feeding movement of the grinding wheel I2, as controlled by the dash pot pistons 98 and 99, respectively, continues until an adjustablestop collar I I3 carried by the sleeve I03 engages a fixed stop surface H4 on the rear face of thedash pot cylinder head. A lock collar H5 serves to position the stop collar H3 and to lock the same in adjusted position.

A throttle valve H6 is located in the pipe line 18 and serves to control the exhaust of fluid from the cylinder 49 so as to regulate the speed of movement of the grinding wheel I2 and its supporting wheel slide I I during the rapid approaching or positioning movement thereof.

Theinfeeding continues until the stop H3 engages the stop surface H4 and positively limits the infeeding movement of the grinding wheel I2. The grinding wheel I2 is then allowed to remain in grinding contact with the work piece 2I for a definite predetermined time interval, after which the control valve 64 is reversed again to move the grinding wheel I2 to its rearward or inoperative position. The latter is accomplished by providing an electrical control system including. an electrical time delay relay I40. Power is provided for the electrical control system from a source of power, as indicated by the power lines MI. The time delay relay. I40 is so connected as to regulate and control the shifting movement of the main control or feed control valve 64 so as to control the entire infeeding movement of the grinding wheel I2, namely, to control the overall cycle includingthe rapid approaching movement of the grinding wheel I2, the slower grindr ing infeed of the wheel, and the dwell which occurs thereafter before the grinding Wheel is removed to its rearward or inoperative position A pair of push button switches I21 and I28 are mounted on the front wall of the machine base I0. The push buttons I21 and I28 are arranged to be actuated by a control lever I29 which is pivotally supported on a stud I30 which is fixedly supported on the base ID of the machine. The button I2'I when pushed is arranged to cause a rearward feeding movement of the grinding wheel I2 and its supporting slide II and the push button I28 when actuated serves to start the grinding cycle. The control lever I29 is normally held in a central or inoperative position by means of the spring-pressed plunger I3I on the lever I29 engaging a V-shaped notch I32 formed in the lever supporting bracket, as shown. The springpressed plunger I3I and the V-shaped notch I32 are so shaped and arranged that when the lever I29 is moved either in a counterclockwise direction to initiate an infeeding movement or in a clockwise direction to interrupt the grinding cycle, the lever will automatically be returned to its inoperative or central position by means of the spring-pressed plunger I3I acting upon the V-shaped notch I32 as soon as the operator releases his grasp on the lever I 20.

The time delay relay I40 is one of the standard electrically operated adjustable time delay relays, such asthat known as the Microflex instantaneous reset timer, manufactured by the Eagle Signal Corporation of Moline, Illinois. The Microflex timer is a synchronous motor operated time delay relay and consists of a clutch-operating mechanism and a motor and gear train assembly, with an electromagnetically operated clutch for coupling them together. It is entirely automatic in action and requires only the closing or opening of the timer control circuit to initiate a cycle of operation. The cycle is initiated by nates, thereby breaking the circuit, the solenoid 8| is deenergized which releases the compression of the spring 86 to reverse the control valve 6 2 and cause a rearward movement of the wheel slide I I and the grinding wheel I2. The timer automatically resets for the next grinding cycle. If for any reason it is desired to stop grinding during a grinding cycle, the lever I29 is moved in a clockwise direction (Fig. 1) instantaneously to open the push button switch ,IZI whichopens a circuit to interrupt the time delay relay and cause the grinding wheel to move to a rearward position.

The time delay relay may be adjusted to control the entire approaching and infeeding movement of the grinding wheel, that is, the rapid approach, grinding feed and dwell. The relay I43 allows a certain time interval to elapse after the push button I28 is actuated to initiate the forward movement of the grinding wheel I2 and to control the dwell thereafter so as to grind the work piece to the desired and predetermined size. The time delay relay Mill is so connected with the push buttons l2? and E28 and also with the solenoid 8! that when the lever 52s is rocked in a counterclockwise direction to start a grind ing cycle, the push button switch E28 is actuated to start the time delay relay. Hi6 functioning and at the same time energizes the solenoid BI which serves to shift the control valve'td toward the left against the compression of the spring 8% to admit fluid under pressure from the pipe 63 through the passage 15, into the cylinder chamber 55, to cause the grinding wheel i2 and its supporting slide Il rapidly to approach the work piece 2| at a rate governed by the throttle valve H6 located in the exhaust pipe line 73. The rapid approaching movement of the grinding wheel I2 and its supporting slide ii continues until the sleeve I93 and its flange Hill engage the dash pot pistons 98 and 9%, respectively, after which the rapid approaching movement caused by the fluid pressure operated piston 52 is slowed down to a slow uniform grinding speed as controlled by the exhaust of fluid from the dash pot cylinders 96 and 9?, respectively, through a needle valve I08, into the reservoir Ill]. The slow grinding'infeed continues until the adjustable stop H3 engages the stop surface I M which positively limits the grinding infeed and allows the grinding wheel i2 to remain in grinding contact with the work piece 2! to finish grind the work.

After a predetermined time interval has elapsed according to the adjustment of the time delay relay M9, the solenoid 8| is automatically deenergized, thereby releasing the compressed spring'80 which returns the control valve 54 into the position illustrated in the drawing so that fluid under pressure passing through the pipe 63 passes through a passage I2 into the cylinder chamber 5% to cause the wheel slide I I and grind- .ing wheel It to move rapidly to their rearward or inoperative position.

The push button I2? is provided so that if for any reason is desirable to interrupt the grinding cycle and cause the grinding wheel IE to move re 'ardly without completing its cycle, the lever 223 may at any time during the grinding cycle be moved in a clockwise direction to operate the push button switch 521 which serves through the'time delay relay Hill to deenergize the solenoid El and thus allow the released compression of the spring 88 to shift the valve 64 .into

the position shown in the drawing so that the grinding wheel I2 will move rapidly to its rear-.- most inoperative position.

The operation of this Wheel feeding mechanism will be readily apparent from the foregoing disclosure. Assuming the various valves and other parts to have been previously adjusted to the desired positions for producing a predetermined grinding cycle, the lever I29 is moved in a counterclockwise direction to actuate the push button switch I28 which serves to set the time delay relay I46 in operation and at the same time energizes the solenoid SI to initiate a forward movement of the grinding wheel I2 and wheel slide II. The approaching movement of the wheel continues first at a rapid rate as determined by the valve H6 and is thereafter slowed down to a grinding feed by means of the dash pot pistons 98 and 99 which continues until the collar m5 engages the sleeve I03 to render the dash pots operative to slow down the rapid approach to a grinding feed of the wheel toward the work piece 25. The needle valve I08 controls the initial grinding feed which continues until the dash pot piston closes the port IIl'I. After the port Iiil is closed, the valve HI controls a line or final grinding feed of the grinding wheel. When the port I01 closes, the screw I24 opens the limit switch I23 to deenergize the solenoid l22, and the released compression of the spring I29 closes the valve H8 to prevent leakage of fluid through the port It! and the needle valve IE8 during the final feed. The final feed continues until the stop collars H3 engage the stop surface H4 positively to prevent further infeeding movement of the grinding wheel. The wheel remains in grinding contact with the work for a period of dwell to finish grind the work piece, after which the time delay relay operates to deenergize the solenoid 8|,- thereby releasing the tension of the spring which moves the control valve 64 toward the right to initiate a rearward feeding movement of the grinding wheel.

It will be readily apparent that the time delay relay it controls the duration of the approaching movement of the wheel and also the period of dwell which follows it. By adjusting the valves H6, I08 and ill, the approaching and grinding feed of the wheel may be independently adjusted, and by manipulation of the time delay relay the over-allcycle, that is, the approching and grinding feeds plus the period of dwell, may also be adjusted so that the entire cycle is under a definite time control.

It may be desirable for certain grinding operations to cut out the automatic cycle control and control the forward and rearward feeding movements of the grinding wheel I2 manually. This may be accomplished by placing a snap switch I35 in the electrical circuit. If it is desired to operate the wheel I2 under the control of the manually operable lever I29, the snap switch H35 is opened, thus rendering the time relay inoperative. In this condition of the electrical circuit, movement of the lever I29 in a counterclockwise direction operates the push button I28 to energize the solenoid 8I to initiate a forward approaching movement of thegrinding wheel I2. Similarly, when the lever I29 is moved in a clockwise direction to operate the push button switch I21, the circuit is broken, thereby deenergizing solenoid BI, which serves through the released compression of the spring 80 to shift the control valve 64 into its reverse position to cause the grinding wheel l2 and its supporting slide H to move to a rearward position.

It will thus be seen that there has been provided by this invention apparatus in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As many possible embodiments may be made of the above invention and as many changes might be made in the em.- bodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawing is to be interpreted as illusti ative and not in a limiting sense.

We claim:

1. In a grinding machine having a transversely movable slide, a rotatable grinding wheel, means including a piston and cylinder rapidly to move said slide and grinding wheel transversely in either direction to position the grinding wheel relative to a work piece to be ground, means operative after a rapid advancing movement of the grinding wheel to produce a slower initial grinding feed of the grinding wheel, a solenoid valve to reduce the rate of infeed, an electric switch to control said solenoid, and adjustable means which is adjustably supported relative to and movable with said piston and wheel slide for actuating said switch after a predetermined initial feed so as to produce a slower final or finishing feed of the grinding wheel.

2. In a grinding machine having a transversely movable wheel slide, a rotatable grinding wheel thereon, means including a piston and cylinder rapidly to move said slide and grinding wheel transversely, and a self-contained dash pot feed regulator associated therewith including a reservoir, the dash pot piston and cylinder, adjustable connections to render said dash pot piston operative after a predetermined advance of the grinding wheel to produce a predetermined grinding feed of the wheel, an adjustable valve connected between said dash pot cylinder and said reservoir to control the initial grinding feed, a solenoid valve between said dash pot cylinder and said reservoir, and electrically controlled means actuated by and in timed relation with the piston after a predetermined initial grinding feed to actuate said solenoid valve so that the first of said valves thereafter regulates the exhaust of fluid from the dash pot cylinder to produce a fine or final grinding feed of the grinding wheel.

3. In a grinding machine having a transversely movable wheel slide, a rotatable grinding wheel, means including a piston and cylinder rapidly to move said slide and grinding wheel transversely in either direction, and a self-contained dash pot regulator associated therewith including a reservoir, a dash pot piston and cylinder, adjustable connections to render said dash pot piston operative after a predetermined advance of the grinding wheel to produce a grinding feed of the wheel, a pair of adjustable independent valves between said dash pot cylinder and said reservoir to control the exhaust of fluid from the dash pot cylinder, thereby to regulate the initial grinding feed, a solenoid valve between one of said valves and the reservoir, means including a limit switch to control said solenoid valve, and means actuated by and in timed relation with the dash pot piston to actuate said switch and thereby close the solenoid valve during the final grinding feed to prevent leakage of fluid from the dash pot cylinder from escaping through the first of said valves.

4. In a grinding machine having a transversely movable wheel slide, a rotatable grinding wheel, means including a piston and cylinder rapidly to move said slide and grinding wl'leel transversely in either direction, and a self-contained dash pot regulator associated therewith including a reservoir, a dash pot piston and cylinder, adjustable connections to render said dash pot piston operative after a predetermined advance of the grinding wheel to produce a grinding wheel feed of the wheel, a pair of adjustable independent valves between said dash pot cylinder and said reservoir to control the exhaust of fluid from the dash pot cylinder, thereby to regulate the initial grinding feed, a solenoid valve between one of said valves and the reservoir, a limit switch to energize said solenoid to hold said solenoid valve open during the initial grinding feed, and means actuated by and in timed relation with the dash pot piston to actuate said switch and thereby close the solenoid valve during the final grinding feed to prevent leakage of fluid from the dash pot cylinder from escaping through the first of said valves.

5. In a grinding machine having a transversely movable wheel slide, a rotatable grinding wheel, means including a piston and cylinder rapidly to move said slide and grinding wheel transversely in either direction, and a self-contained dash pot regulator associated therewith including a reservoir, a dash pot piston and cylinder, adjustable connections to render said dash pot piston operative after a predetermined advance of the grinding wheel to produce a grinding feed of the wheel, a pair of adjustable independent valves between said dash pot cylinder and said reservoir to control the exhaust of fluid from the dash pot cylinder, thereby to regulate the initial grinding feed, a solenoid valve between one of said valves and the reservoir, a normally closed limit switch to energize said solenoid to hold said solenoid valve open during the initial grinding feed, and means actuated by and in timed relation with the dash pot piston to actuate said switch and thereby close the solenoid valve during the final grinding feed to prevent leakage of fluid from the dash pot cylinder from escaping through the first of said valves.

CARL G. FLYGARE. WALTER F. JOHNSON. 

